If you have a thermometer with a silvery ball of mercury inside, now is the time to properly dispose of it.

Hamilton County public health officials have revived a mercury thermometer exchange program. The program encourages people to swap their mercury thermometers for a free digital one.

First tried in 2002, the program collected more than 4,500 mercury thermometers and distributed 3,500 electronic thermometers that year.

County officials opted for a general household waste collection program last year that scooped up paints and pesticides, but the number of mercury thermometers turned in by residents was low.

So the focus is back on mercury. Throughout May, officials hope to distribute more than 5,000 thermometers at 12 exchange sites throughout Hamilton County.

The county spent $10,000 to purchase the thermometers.

Mercury is highly toxic. If released into the environment, mercury from a broken thermometer can cause nausea, shortness of breath and severe headaches. Intense exposure may cause vision, hearing and speech impairment, respiratory problems and even death.

Children are the most sensitive to mercury poisoning.

The Cincinnati Drug and Poison Information Center at Cincinnati Children's Hospital Medical Center received 438 calls about mercury thermometers last year. Of those, 266 calls posed general questions about the devices, and 172 dealt with mercury exposures - skin contact, inhalation and ingestion.

"We don't want people to simply throw away their old thermometers once they hear about the dangers of mercury," said Hamilton County Health Commissioner Tim Ingram. "The thermometer may break in disposal."

To help ensure safety, all mercury thermometers should be placed inside two sealed plastic bags when they are brought to an exchange site, Ingram said.

Thermometers can be exchanged 9 a.m.-4 p.m. Monday through Friday at participating sites.

To locate an exchange site near you, call the Mercury Hotline, (513) 946-7788, or visit www.hcdoes.org/sw/mercury.htm.